Glaze composition and antifouling ceramic ware

ABSTRACT

A glaze composition can be used to provide a glaze layer having excellent antifouling performance and visual beauty. The glaze composition contains a glaze forming material, which has a composition determined such that a baked product obtained by baking the glaze composition comprises 55.0 to 67.0 wt % of SiO 2 ; 8.0 to 11.0 wt % of Al 2 O 3 ; 2.0 to 8.0 wt % of SnO 2 ; 15.0 to 21.0 wt % of a divalent metal oxide; and 4.0 to 6.0 wt % of a monovalent metal oxide, with respect to a total weight of the baked product. When a glaze layer is formed by use of this glaze composition, it resists contamination. Even when a dirt deposits on the glaze layer, the dirt can be easily removed from the glaze layer. In addition, the glaze composition can provide a beautiful semi-opaque glaze layer with luster and a reduction in pore generation amount.

TECHNICAL FIELD

The present invention relates to a glaze composition, which ispreferably used to form a glaze layer having excellent antifoulingperformance and good appearance, and an antifouling ceramic ware havingthe glaze layer.

BACKGROUND ART

Glazes are widely used to protect ceramic wares from contamination andprovide beautiful appearance of the ceramic wares. In general, a glazelayer can be formed on a ceramic ware by applying a glaze thereon, andbaking the applied glaze. Thus, since the glaze layer presentsresistance to contamination and the beautiful appearance to the ceramicware, it is being widely used in application areas of ceramic sanitarywares for toilets and bathrooms as well as general ceramic wares.

However, when the conventional glazes are used, there are problems thata yet-to-be dissolved substance easily remains in the glaze layer, orzirconium silicate of an emulsion agent is crystallized to appear on theoutermost surface of the glaze layer. As a consequence, a beautiful,smooth surface with luster of the glaze layer can not be obtained.

In addition, there is a room for further improvement of the antifoulingperformance of the glaze layer. For example, to improve the antifoulingperformance, it is proposed to form a transparent glaze layer consistingof amorphous materials. In this case, the antifouling performance can beimproved to some extent. However, it becomes difficult to provide thebeautiful appearance of the glaze layer to articles because of thetransparency of the glaze layer. Due to this reason, it will benecessary to form another glaze layer having a desired color between thetransparent glaze layer and the ceramic ware. This two-layer structureleads to an increase in production time and cost.

In addition, in the case of using tin oxide or bone ash as the emulsionagent in conventional glazes for ceramic ware, there are problems thatpore generation amount in the glaze layer after baking increases, and abeautiful semi-opaque glaze layer is not obtained by baking. Forexample, it is proposed to use a glaze having the composition of 80 wt %of SiO₂; 6.5 wt % of Al₂O₃; 0.2 wt % of Fe₂O₃; 0.8 wt % of MgO; 8 wt %of CaO; 3 wt % of ZnO; 1 wt % of K₂O; 0.5 wt % of NaO; 5 wt % of SnO₂(median diameter: 5 μm). However, this glaze is not melted even whenbaked at the temperature of 1200° C. In addition, there is a room ofimprovement in the antifouling performance and a degree of luster of theglaze layer.

SUMMARY OF THE INVENTION

In view of the above fact, a purpose of the present invention is toprovide a glaze composition having the capability of forming a glazelayer that is excellent in resistance to contamination and easiness ofremoving dirt and has a beautiful appearance, and antifouling ceramicwares having the glaze layer.

That is, a glaze composition of the present invention is characterizedby containing a glaze forming material, which has a compositiondetermined such that a baked product obtained by baking the glazecomposition comprises 55.0 to 67.0 wt % of SiO₂; 8.0 to 11.0 wt % ofAl₂O₃; 2.0 to 8.0 wt % of SnO₂; 15.0 to 21.0 wt % of a divalent metaloxide; and 4.0 to 6.0 wt % of a monovalent metal oxide, with respect toa total weight of the baked product.

It is preferred that the glaze composition contains the glaze formingmaterial having the capability of forming a glaze layer by baking, andthe glaze forming material comprises, with respect to a total weight ofthe glaze forming material,

-   (a) 55.0 to 67.0 wt % of silicon constituent by SiO₂ conversion;-   (b) 8.0 to 11.0 wt % of aluminum constituent by Al₂O₃ conversion;-   (c) 2.0 to 8.0 wt % of tin constituent by SnO₂ conversion;-   (d) 15.0 to 21.0 wt % of a divalent metal constituent by oxide    conversion; and-   (e) 4.0 to 6.0 wt % of a monovalent metal constituent by oxide    conversion.

In particular, It is preferred that the glaze composition contains theglaze forming material, which comprises, with respect to a total weightof the glaze forming material,

-   (a) 63.0 to 67.0 wt % of silicon constituent by SiO₂ conversion;-   (b) 8.0 to 10.0 wt % of aluminum constituent by Al₂O₃ conversion;-   (c) 2.0 to 4.0 wt % of tin constituent by SnO₂ conversion;-   (d) 16.0 to 20.0 wt % of a divalent metal constituent by oxide    conversion; and-   (e) 4.0 to 6.0 wt % of a monovalent metal constituent by oxide    conversion.

In addition, it is preferred that the constituent (d) comprises, withrespect to the total weight of the glaze forming material,

-   (d1) 10.0 to 12.0 wt % of calcium constituent by CaO conversion; and-   (d2) 5.0 to 8.0 wt % of zinc constituent by ZnO conversion.

It is also preferred that the constituent (d) comprises (d3) 1.0 wt % orless of magnesium constituent by MgO conversion, with respect to thetotal weight of the glaze forming material.

It is further preferred that the monovalent metal constituent (e)comprises, with respect to the total weight of the glaze formingmaterial,

-   (e1) 1.0 wt % or more of sodium constituent by Na₂O conversion; and-   (e2) 1.0 wt % or more of potassium constituent by K₂O conversion.

In a preferred embodiment of the present invention, the glaze formingmaterial comprises a frit, which is obtained by vitrifying a materialcontaining at least one of the constituents (a) to (e) and grinding thevitrified material.

It is preferred that a material containing the constituent (a) of theglaze forming material is a powder having a particle size of 30 μm orless.

It is preferred that a material containing the constituent (c) of theglaze forming material is a powder having a median diameter of 0.2 to4.0 μm.

It is also preferred that a median diameter after grinding and mixing ofthe glaze forming material is within a range of 4 to 5 μm.

In addition, it is preferred that the glaze forming material containedin the glaze composition is prepared by grinding a material containingat least one of the constituents (a) and (c) to obtain a powder or aslurry, then mixing materials containing the remaining constituents withthe powder or the slurry, and grinding a resultant mixture to obtain apowder of the glaze forming material having a required particle size ora slurry thereof.

It is preferred that the glaze forming material is prepared by grindinga material containing the constituent (a) to obtain a powder having amedian diameter of 5 μm or less or a slurry thereof, then mixingmaterials containing the remaining constituents (b) to (e) with thepowder or the slurry, and grinding a resultant mixture to obtain apowder of the glaze forming material having a required particle size ora slurry thereof.

It is preferred that the glaze forming material is prepared by grindinga material containing the constituent (c) to obtain a powder having amedian diameter of 1.5 to 2 μm or a slurry thereof, then mixingmaterials containing the remaining constituents (a), (b), (d) and (e)with the powder or the slurry, and grinding a resultant mixture toobtain a powder of said glaze forming material having a requiredparticle size or a slurry thereof.

It is preferred that the glaze forming material is prepared by grindingmaterials containing the constituents (a) and (c) to obtain a mixedpowder having a median diameter of 5 μm or less or a slurry thereof,then mixing materials containing the remaining constituents (b), (d) and(e) with the mixed powder or the slurry, and grinding a resultantmixture to obtain a powder of the glaze forming material having arequired particle size or a slurry thereof.

It is also preferred that the glaze forming material is prepared bygrinding a material containing the constituent (a) to obtain a powderhaving a median diameter of 5 μm or less or a slurry thereof, thenmixing materials containing the remaining constituents (b) to (e) withthe powder or the slurry, and grinding a resultant mixture to obtain apowder of the glaze forming material having a median diameter of 4 to 5μm or a slurry thereof.

It is further preferred that the glaze forming material is prepared bygrinding a material containing the constituent (c) to obtain a powderhaving a median diameter of 1.5 to 2 μm or a slurry thereof, then mixingmaterials containing the remaining constituents (a), (b), (d) and (e)with the powder or the slurry, and grinding a resultant mixture toobtain a powder of the glaze forming material having a median diameterof 4 to 5 μm or a slurry thereof.

It is preferred that the glaze forming material is prepared by grindingmaterials containing the constituents (a) and (c) to obtain a mixedpowder having a median diameter of 5 μm or less or a slurry thereof,then mixing materials containing the remaining constituents (b), (d) and(e) with the mixed powder or the slurry, and grinding a resultantmixture to obtain a powder of the glaze forming material having a mediandiameter of 4 to 5 μm or a slurry thereof.

Moreover, it is preferred that the materials containing the constituentsof said glaze forming material are ground by means of ball milling usingalumina balls. In particular, it is preferred that materials containingthe constituents of the glaze forming material are ground by means ofball milling using a pot with an alumina liner and alumina balls.

It is preferred that the glaze composition comprises a pigment.

Another object of the present invention is to provide an antifoulingceramic ware, which is produced by forming a layer of the glazecomposition of the present invention on a dried base surface of a rawceramic ware, and baking the layer at a temperature of 1150 to 1250° C.for 8 hours or more to form a glaze layer on a baked base surface of theceramic ware.

In a preferred embodiment of the present invention, an X-ray diffractionprofile of the glaze layer of the antifouling ceramic ware has onlydiffraction peaks resulting from SnO₂ crystal. Alternatively, it ispreferred that an X-ray diffraction profile of the glaze layer has onlydiffraction peaks resulting from CaSnSiO₅ crystal. Moreover, it ispreferred that an X-ray diffraction profile of the glaze layer has onlydiffraction peaks resulting from crystals of SnO₂ and CaSnSiO₅.

In addition, it is preferred that a thickness of the glaze layer iswithin a range of 0.2 to 1.2 mm.

These and still other objects and advantages will become apparent fromthe following detail description and Examples of the invention,referring to the attached drawings.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1A is an X-ray diffraction profile of a glaze layer of Example 1,and

FIG. 1B is a diagram showing a relation between the X-ray diffractionprofile of FIG. 1A and an X-ray diffraction profile of SnO₂ crystalobtained by simulation;

FIG. 2A is an X-ray diffraction profile of a glaze layer of Example 2,and

FIG. 2B is a diagram showing a relation between the X-ray diffractionprofile of FIG. 2A and an X-ray diffraction profile of SnO₂ and SnSiO₆crystals obtained by simulation; and

FIG. 3A is an X-ray diffraction profile of a glaze layer of ComparativeExample 1, and FIG. 3B is a diagram showing a relation between the X-raydiffraction profile of FIG. 3A and an X-ray diffraction profile of azirconium silicate crystal obtained by simulation.

DETAIL DESCRIPTION OF THE INVENTION

A glaze composition of the present invention contains a glaze formingmaterial. To improve easiness of applying the glaze composition onarticles, for example, articles of base materials for ceramic wares, theglaze composition may preferably contain water and/or various binders.

The glaze forming material of the present invention comprises siliconconstituent, aluminum constituent, tin constituent, a divalent metalconstituent, and a monovalent metal constituent. The composition of theglaze forming material is determined such that a baked product obtainedby baking the glaze composition comprises 55.0 to 67.0 wt % of SiO₂; 8.0to 11.0 wt % of Al₂O₃; 2.0 to 8.0 wt % of SnO₂; 15.0 to 21.0 wt % of adivalent metal oxide; and 4.0 to 6.0 wt % of a monovalent metal oxide,with respect to a total weight of the baked product. In other words, thecontents of these constituents are determined so as to comprise, withrespect to a total weight of the glaze forming material, (a) 55.0 to67.0 wt % of silicon (Si) constituent by SiO₂ conversion; (b) 8.0 to11.0 wt % of aluminum (Al) constituent by Al₂O₃ conversion; (c) 2.0 to8.0 wt % of tin (Sn) constituent by SnO₂ conversion; (d) 15.0 to 21.0 wt% of the divalent metal constituent by oxide conversion; and (e) 4.0 to6.0 wt % of the monovalent metal constituent by oxide conversion.

When the content of the Si constituent is less than 55.0 wt %, theantifouling performance of the glaze layer can not be sufficientlyobtained. In addition, there is a case that the appearance of the glazelayer deteriorates because of an increase in pore generation amount anda degradation of color (semi-opaque) of the glaze layer. On the otherhand, when the content of the Si constituent is more than 67.0 wt %, theantifouling performance of the glaze layer deteriorates. In addition,the pore generation amount increases, and the degradation of color(semi-opaque) of the glaze layer occurs.

When the content of the Al constituent is less than 8.0 wt %, theantifouling performance of the glaze layer can not be sufficientlyobtained, and the pore generation amount in the glaze layer increases.On the contrary, when the content of the Al constituent is more than11.0 wt %, an effect of improving the color (semi-opaque) of the glazelayer, which is brought by the presence of the Sn constituent in theglaze forming material, is prevented.

When the content of the Sn constituent is less than 2.0 wt %, the color(semi-opaque) of the glaze layer can not be sufficiently improved. Whenthe content of the Sn constituent is more than 8.0 wt %, the antifoulingperformance of the glaze layer deteriorates.

When the contents of the divalent metal constituent is less than 15.0 wt%, or the content of the monovalent metal constituent is less than 4.0wt %, a vitrification of the glaze forming material is prevented at abaking step described later. This leads to insufficient antifoulingperformance. In addition, the luster of the glaze layer becomes poor. Onthe contrary, when the content of the divalent metal constituent is morethan 21.0 wt %, or the content of the monovalent metal constituent ismore than 4.0 wt %, the antifouling performance deteriorates, and thepore generation amount in the glaze layer increases.

As the divalent metal constituent, for example, calcium (Ca)constituent, zinc (Zn) constituent, and/or magnesium (Mg) constituentcan be used. In particular, it is preferred that the glaze formingmaterial comprises, as the divalent metal constituent, (d1) 10.0 to 12.0wt % of calcium constituent by CaO conversion; and (d2) 5.0 to 8.0 wt %of zinc constituent by ZnO conversion, with respect to the total weightof the glaze forming material. In this case, it is possible to stablyobtain the improved antifouling performance and the luster of the glazelayer.

In addition, when the contents of the Ca and Zn constituents are withinthe above ranges, a small amount of the Mg constituent may be containedin the glaze forming material. That is, it is preferred that the contentof the Mg constituent is less than 1.0 wt % of magnesium constituent byMgO conversion, with respect to the total weight of the glaze formingmaterial. The lower limit of the content of the Mg constituent is notlimited. For example, it may be 0.1 wt %.

As the monovalent metal constituent, for example, sodium (Na)constituent and/or potassium (K) constituent, can be used. Inparticular, it is preferred that the glaze forming material comprises,as the monovalent metal constituent, (e1) 1.0 wt % or more of sodiumconstituent by Na₂O conversion; and (e2) 1.0 wt % or more of potassiumconstituent by K₂O conversion, with respect to the total weight of theglaze forming material. In this case, it is possible to obtain the glazelayer with good luster and further improve the antifouling performance.When the content of the Na constituent is substantially equal to thecontent of K constituent, better results are obtained. In considerationof the content of the monovalent metal constituent, which is within therange of 4.0 to 8.0 wt %, the upper limit of the content of each of theNa and K constituents may be 4 wt %, and preferably 3 wt %.

It is particularly preferred that the contents of these constituents aredetermined to comprise, with respect to a total weight of the glazeforming material, (a) 63.0 to 67.0 wt % of silicon constituent by SiO₂conversion; (b) 8.0 to 10.0 wt % of aluminum constituent by Al₂O₃conversion; (c) 2.0 to 4.0 wt % of tin constituent by SnO₂ conversion;(d) 16.0 to 20.0 wt % of a divalent metal constituent by oxideconversion; and (e) 4.0 to 6.0 wt % of a monovalent metal constituent byoxide conversion. In other words, the composition of the glaze formingmaterial is determined such that a baked product obtained by baking theglaze composition comprises 63.0 to 67.0 wt % of SiO₂; 8.0 to 10.0 wt %of Al₂O₃; 2.0 to 4.0 wt % of SnO₂; 16.0 to 20.0 wt % of the divalentmetal oxide; and 4.0 to 6.0 wt % of the monovalent metal oxide, withrespect to a total weight of the baked product.

Usually, a raw material containing the Sn constituent is more expensivethan the raw materials containing the other constituents. Therefore, asthe amount used of the raw material containing the Sn constituentreduces, the total cost performance of the glaze composition can beimproved. Even when the content of the Sn constituent is within therange of 2.0 to 4.0 wt %, the beautiful semi-opaque glaze layer can bestill obtained because the glaze forming material contains at least 63.0wt % of the Si constituent. Thus, by reducing the content of the Snconstituent, it is possible to provide the glaze composition havingexcellent cost performance.

On the other hand, when the content of the divalent metal constituent iswithin the range of 16.0 to 20.0 wt %, and the content of the monovalentmetal constituent is within the range of 4.0 to 6.0 wt %, it is possibleto further improve the antifouling performance and the luster of theglaze layer.

Each of the constituents of the glaze forming material can be providedin the form of an oxide thereof. Alternatively, a raw materialcontaining the constituent in the form other than the oxide may be usedto prepare the glaze composition. That is, it is possible to use the rawmaterial satisfying the condition that an oxide of the constituent canbe generated in the glaze layer when the constituent in the raw materialis oxidized by baking. Concretely, feldspars, silica, limestone,dolomite, zinc oxide, “Gairome” clay and a tin-oxide powder can be used.Therefore, the glaze forming material can be prepared by grinding andmixing required amounts of these materials.

In addition, it is preferred than the glaze forming material contains afrit. For example, the frit can be prepared by melting a mixture ofcompounds containing the required constituents described above,vitrifying the mixture, and grinding the vitrified (amorphous) material.Of course, the frit prepared by using some of the constituents may bemixed with the remaining constituent(s). The glaze composition can beobtained by mixing the glaze forming material with a required amount ofwater and a binder, if necessary.

It is preferred to preliminarily control the particle size of the rawmaterial containing the Si or Sn constituent to prepare the glazeforming material. For example, a preliminary grinding step for the rawmaterial containing the Si constituent such as the feldspars or silicamay be performed. By classifying a resultant product, a powder notcontaining particles of more than 30 μm or a slurry thereof can beobtained. In addition, the preliminary grinding step for the rawmaterial containing the Sn constituent such as a tin-oxide powder may beperformed. By classifying a resultant product, a powder having of amedian diameter of 0.2 to 4.0 μm or a slurry thereof can be obtained.These cases are effective to stably obtain the effects of improving theantifouling performance and the visual beauty of the glaze layer. Themedian diameter is defined as a particle size corresponding to 50% of acumulative curve in particle-size distribution, which is also named as50% average particle size (D50). In the present specification, themedian diameter is determined according to the particle-sizedistribution based on weight. In this case, a total weights of particleshaving diameters larger than the median diameter is equal to the totalweight of the particles having diameters smaller than the mediandiameter.

In addition, it is preferred that a median diameter of the glaze formingmaterial is within a range of 4 to 5 μm. When the range of mediandiameter is satisfied, it is possible to further improve the antifoulingperformance and a degree of luster of the glaze layer.

In the case of preparing the glaze composition of the present invention,it is preferred to preliminarily grind a raw material containing atleast one of the Si and Sn constituents to obtain a powder or a slurry,mix raw materials containing the remaining constituents with the powderor the slurry, and grind a resultant mixture to obtain a powder of theglaze forming material having a required particle size or a slurrythereof. When preparing the slurry of the glaze forming material, thesegrinding steps can be performed in the presence of water.

In the case of preliminarily grinding only the raw material containingthe Si constituent, it is preferred to carry out the grinding step toobtain a powder having a median diameter of 5 μm or less or a slurrythereof. Then, the raw materials containing the remaining constituentsare mixed with the powder or the slurry. A resultant mixture is groundagain to obtain a powder of the glaze forming material having a requiredparticle size or a slurry thereof. In this case, it is possible tofurther reduce the pore generation amount, and obtain a better visualbeauty of the glaze layer. As described above, as the median diameter ofthe raw material containing the Si constituent becomes smaller, betterresults are obtained. However, the median diameter of about 1 μm may besuitable from the viewpoint of a reduction in production time.

In the case of preliminarily grinding only the raw material containingthe Sn constituent, it is preferred to carry out the grinding step toobtain a powder having a median diameter of 1.5 to 2 μm or a slurrythereof. Then, the raw materials containing the remaining constituentsare mixed with the powder or the slurry. A resultant mixture is groundagain to obtain a powder of the glaze forming material having a requiredparticle size or a slurry thereof. In this case, it is possible tofurther improve the antifouling performance, and provide a beautifulsemi-opaque glaze layer with good luster. Thus, this preliminarygrinding step is particularly effective to improve the appearance of theglaze layer.

In the case of preliminarily grinding the raw materials containing theSi and Sn constituents, it is preferred to carry out the grinding stepto obtain a mixed powder having a median diameter of 5 μm or less or aslurry thereof. Then, raw materials containing the remainingconstituents with the mixed powder or the slurry. A resultant mixture isground again to obtain a powder of the glaze forming material having arequired particle size or a slurry thereof. In this case, it is possibleto further reduce the pore generation amount, and obtain a better visualbeauty of the semi-opaque glaze layer. As described above, as the mediandiameter of the raw materials containing the Si and Sn constituentsbecomes smaller, better results are obtained. However, the mediandiameter of about 1 μm may be suitable from the viewpoint of a reductionin production time.

After the preliminary grinding step described above, it is preferred togrind the resultant mixture such that the powder of the glaze formingmaterial has a median diameter of 4 to 5 μm or a slurry thereof. In thisrange it is effective to further improve the antifouling performance andthe visual beauty of the semi-opaque glaze layer with luster.

For example, the grinding step may be performed by means of ballmilling. In this case, it is preferred to use alumina or silica ballsfor ball milling and/or a ball-mill pot having a liner made of aluminaor silica. These are useful to prevent contamination of the glazeforming material. In particular, since alumina is excellent in wearresistance, it is possible to minimize a situation that broken pieces ofthe balls are mixed with the glaze forming material during theball-milling step. As a consequence, it leads to excellent antifoulingperformance of the glaze layer. From these reasons, it is recommended touse the balls and liner of alumina.

To improve the easiness of applying the glaze composition, it ispreferred that the glaze composition contains water. For example, about40 parts by weight of water may be used with respect to 100 parts byweight of solid matter in the glaze composition. To enhance the filmformation capability of the glaze composition, the glaze composition maycontain a binder, which can be vaporized during the baking. The kind ofthe binder can be optionally selected.

In the case of forming the glaze layer having a desired color other thansemi-opaque, the glaze composition can contain a pigment for providingthe desired color to the glaze layer. The kind of the pigment can beoptionally selected. However, it is preferred to use the pigment, whichis not crystallized when the glaze layer is formed.

Another important purpose of the present invention is to provide anantifouling ceramic ware having the glaze layer, which is formed by useof the glaze composition of the present invention. That is, theantifouling ceramic ware can be produced according to the followingsteps. First, the glaze composition explained above is applied on arequired surface of a dried article made of a base material for ceramicwares. For example, the glaze composition may be spayed on the article.Next, the applied layer is baked at a temperature of 1150 to 1250° C.for 8 hours or more to form the glaze layer on the surface of the bakedarticle. When the temperature is less than 1150° C., the antifoulingperformance of the glaze layer may deteriorate, and the degree of lusterof the glaze layer may decrease. On the other hand, when the temperatureis more than 1250° C., there is a case that the fluidity of the glazecomposition of the applied layer increases, and variations in thicknessof the glaze layer become wide. When the baking temperature is withinthe above range, it is possible to stably obtain the glaze layer withgood luster and excellent antifouling performance. As the baking time islonger than 8 hours, the pore reduction amount in the glaze layerreduces. However, it is preferred to select the baking time less than 24hours from the viewpoint of a reduction in production cost.

To bake the glaze composition, for example, a roller-heath type furnaceor a tunnel kiln can be used. In the roller-heath type furnace, pluralrollers for traveling the articles to be baked are arranged. On theother hand, in the tunnel kiln, cars carrying the articles to be bakedare movable. In these cases, since large amounts of the articles can besuccessively baked, it is possible to obtain a high productionefficiency. When using the roller-heath type furnace, it is preferred tobake the articles for 8 hours or more. When using the tunnel kiln, it ispreferred to bake the article for 10 hours or more.

In the above production method, it is preferred that the glazecomposition is applied on the required surface of the article such thata thickness of the glaze layer after baking is within a range of 0.2 to1.2 mm. In this range, the surface of the article can be concealedbehind the glaze layer. When the thickness is less than 0.2 mm, thesurface of the article may become visible through the glaze layer. Onthe other hand, when the thickness is more than 1.2 mm, fine cracks mayeasily develop when the applied layer of the glaze composition is driedbefore the baking step. In such a case, there is a fear that a defectthat is the so-called “parting” occurs in the glaze layer after thebaking step, and the surface of the article is partially exposedoutside.

By analyzing the glaze layer of the present invention with an X-raydiffraction analysis method after the baling step, diffraction peaksresulting from SnO₂ and/or CaSnSiO₅ (tin sphene) crystals can bedetected. That is, no diffraction peak resulting from crystals otherthan SnO₂ and CaSnSiO₅ crystals can be detected. It means that most ofthe constituents of the glaze composition makes an amorphous structure.The color (semi-opaque) of the glaze layer is provided by the presenceof the SnO₂ and CaSnSiO₅ crystals. Since the glaze composition of thepresent invention does not contain zirconium constituent, it is possibleto provide a smooth surface with luster of the glaze layer and excellentantifouling performance without surface unevenness of the glaze layer,which is caused by the generation of zirconium silicate (ZrSiO₄)crystals.

EXAMPLES

Next, preferred examples of the present invention are described indetail.

Example 1

As raw materials of a glaze forming material of the present invention,“Kamato” feldspar, silica powder, lime stone, dolomite, zinc oxide,“Gairome” clay and a tin-oxide powder were used. A content of particlesof 30 μm or more in each of the silica powder and “Gairome” clay isabout 2%. The silica powder and “Gairome” clay are the raw materialscontaining the Si constituent. A median diameter of the tin-oxide powderis 4.1 μm.

A required amounts of the raw materials was put in a ball-mill pothaving a silica liner, and then 40 parts by weight of water was added tothe pot with respect to 100 parts by weight of solid matter of the rawmaterials. A resultant mixture was ball-milled for 8 hours by use of theball-mill pot and silica balls. As a consequence, a glaze composition ofExample 1 was obtained. The composition “A” of a glaze forming materialof the obtained glaze composition is shown in Table 1 by oxideconversion. The median diameter of the glaze forming material in theglaze composition was measured by use of an X-ray transmission-typeparticle-size measuring instrument. In Example 1, the median diameter is5.1 μm.

Subsequently, this glaze composition was sprayed on a surface of anarticle of a base material for ceramic sanitary wares to form a layer ofthe glaze composition thereon. The ceramic ware with the sprayed layerwas baked at the maximum temperature of 1200° C. for 16 hours in atunnel kiln to obtain a baked article having a glaze layer of 0.6 mmthickness as the ceramic sanitary ware of Example 1.

Examples 2 to 9, Comparative Examples 1 to 13

In each of Examples 2 to 9 and Comparative Examples 1 to 13, a glazecomposition was prepared according to a substantially same method asExample 1 except that different additive amounts of the raw materialswere used, and the ball-milling step was performed under a differentcondition such that a glaze forming material has the median diameter of5.1 μm. The compositions “B” to “V” of glaze forming materials of theglaze compositions obtained in Examples 2 to 9 and Comparative Examples1 to 13 are shown in Tables 1 and 2 by oxide conversion.

Subsequently, the glaze composition was sprayed on a surface of anarticle of a base material for ceramic sanitary wares to form a layer ofthe glaze composition thereon. The ceramic ware with the sprayed layerwas baked under the same baking conditions as Example 1 to obtain abaked article having a glaze layer of 0.6 mm thickness as the ceramicsanitary ware.

Examples 10, 11

In each of Examples 10 and 11, 30 parts by weight of a glass frit powder(manufactured by Japan Frit Company; Product Number PN-54321; SiO₂: 70wt %, Al₂O₃; 14 wt %, Na₂O: 16 wt %) was added to 70 parts by weight ofthe other raw materials. A resultant mixture was ball-milled by use ofthe same ball-mill pot and balls as Example 1 to obtain a glaze formingmaterial having the median diameter of 5.1 μm. The compositions “A” and“B” of the glaze forming materials of Examples 10 and 11 are shown inTable 1 by oxide conversion.

Subsequently, the glaze composition was sprayed on a surface of anarticle of a base material for ceramic sanitary wares to form a layer ofthe glaze composition thereon. The ceramic ware with the sprayed layerwas baked under the same baking conditions as Example 1 to obtain abaked article having a glaze layer of 0.6 mm thickness as the ceramicsanitary ware.

Examples 12, 13

In these Examples, raw materials of the “Kamato” feldspar and silicapowder were preliminarily grounded and classified to remove largeparticles of 30 μm or more therefrom. Except for the above step, glazecompositions of Examples 12 and 13 were prepared according to thesubstantially same methods as Example 1 or 2, respectively. The obtainedglaze composition contains a glaze forming material having the mediandiameter of 5.1 μm. The compositions “A” and “B” of the glaze formingmaterials of Examples 12 and 13 are shown in Table 1 by oxideconversion.

Next, the glaze composition was sprayed on a surface of an article of abase material for ceramic sanitary wares to form a layer of the glazecomposition thereon. The ceramic ware with the sprayed layer was bakedunder the same baking conditions as Example 1 to obtain a baked articlehaving a glaze layer of 0.6 mm thickness as the ceramic sanitary ware.

Examples 14 to 17

In each of Examples 14 and 15, a glaze composition was preparedaccording to the substantially same method as Example 3 except that atin-oxide powder having a median diameter of 3.2 μm (Example 14) or 0.1μm (Example 15) was used as the raw material containing Sn constituent,as shown in Table 3. The obtained glaze composition contains a glazeforming material having the median diameter of 5.1 μm. The composition“C” of the glaze forming material of Examples 14 and 15 is shown inTable 1 by oxide conversion.

In each of Examples 16 and 17, a glaze composition was preparedaccording to the substantially same method as Example 4 except that atin-oxide powder having a median diameter of 3.2 μm (Example 16) or 0.1μm (Example 17) was used as the raw material containing Sn constituent,as shown in Tables 3 and 4. The obtained glaze composition contains aglaze forming material having the median diameter of 5.1 μm. Thecomposition “D” of the glaze forming material of Examples 16 and 17 isshown in Table 1 by oxide conversion.

Next, the glaze composition was sprayed on a surface of an article of abase material for ceramic sanitary wares to form a layer of the glazecomposition thereon. The ceramic ware with the sprayed layer was bakedunder the same baking conditions as Example 1 to obtain a baked articlehaving a glaze layer of 0.6 mm thickness as the ceramic sanitary ware.

Examples 18, 19

In each of Examples 18 and 19, a glaze composition was preparedaccording to the substantially same method as Example 2 except that themedian diameter of the glaze forming material was adjusted to 4.3 μm(Example 18) or 3.8 μm (Example 19) by controlling the ball-millingtime, as shown in Table 4. The composition “B” of the glaze formingmaterial of Examples 18 and 19 is shown in Table 1 by oxide conversion.

Next, the glaze composition was sprayed on a surface of an article of abase material for ceramic sanitary wares to form a layer of the glazecomposition thereon. The ceramic ware with the sprayed layer was bakedunder the same baking conditions as Example 1 to obtain a baked articlehaving a glaze layer of 0.6 mm thickness as the ceramic sanitary ware.

Examples 20 to 22

One (Examples 20, 21) or both (Example 22) of raw materials containingSi and Sn constituents was mixed with 20 parts by weight of water toobtain a first mixture, and then the first mixture was preliminarilyball-milled for 1 hour by use of the same ball-mill pot and balls asExample 1, so that the median diameters of these raw materials becamethe values shown in Table 4. The remaining raw materials and water wereadded into the pot having the first mixture therein, and a resultantmixture was ball-milled to obtain a glaze composition. A content ofwater is 40 parts by weight with respect to 100 parts by weight of thesolid matter of the raw materials. The obtained glaze compositioncontains a glaze forming material having the median diameter of 5.1 μm.The composition “B” of the glaze forming material of Examples 20 to 22is shown in Table 1 by oxide conversion.

Next, the glaze composition was sprayed on a surface of an article of abase material for ceramic sanitary wares to form a layer of the glazecomposition thereon. The ceramic ware with the sprayed layer was bakedunder the same baking conditions as Example 1 to obtain a baked articlehaving a glaze layer of 0.6 mm thickness as the ceramic sanitary ware.

Example 23

A raw material containing Si constituent was mixed with 20 parts byweight of water to obtain a first mixture, and then the first mixturewas preliminarily ball-milled for 4 hours by use of the same ball-millpot and balls as Example 1, so that the median diameters of the rawmaterial became 5.0 μm. The remaining raw materials and water were addedinto the pot having the first mixture therein, and then a resultantmixture was ball-milled for 7 hours to obtain a glaze composition. Acontent of water is 40 parts by weight with respect to 100 parts byweight of the solid matter of the raw materials. The obtained glazecomposition contains a glaze forming material having the median diameterof 4.4 μm. The composition “B” of the glaze forming material of Examples23 is shown in Table 1 by oxide conversion.

Next, the glaze composition was sprayed on a surface of an article of abase material for ceramic sanitary wares to form a layer of the glazecomposition thereon. The ceramic ware with the sprayed layer was bakedunder the same baking conditions as Example 1 to obtain a baked articlehaving a glaze layer of 0.6 mm thickness as the ceramic sanitary ware.

Examples 24 and 25

In each of Examples 24 and 25, a raw material containing Sn constituentwas mixed with 20 parts by weight of water to obtain a first mixture,and then the first mixture was preliminarily ball-milled for 3 hours(Example 24) or 6 hours (Examples 25) by use of the same ball-mill potand balls as Example 1, so that the median diameters of the raw materialbecame 1.8 μm (Example 24) or 1.3 μm (Example 25). The remaining rawmaterials and water were added into the pot having the first mixturetherein, and then a resultant mixture was ball-milled for 7 hours toobtain a glaze composition. A content of water is 40 parts by weightwith respect to 100 parts by weight of the solid matter of the rawmaterials. The obtained glaze composition contains a glaze formingmaterial having the median diameter of 4.9 μm. The composition “B” ofthe glaze forming material of Examples 24 and 25 is shown in Table 1 byoxide conversion.

Next, the glaze composition was sprayed on a surface of an article of abase material for ceramic sanitary wares to form a layer of the glazecomposition thereon. The ceramic ware with the sprayed layer was bakedunder the same baking conditions as Example 1 to obtain a baked articlehaving a glaze layer of 0.6 mm thickness as the ceramic sanitary ware.

Example 26

Both of raw materials containing Si and Sn constituent were mixed with20 parts by weight of water to obtain a first mixture, and then thefirst mixture was preliminarily ball-milled for 4 hours by use of thesame ball-mill pot and balls as Example 1, so that the median diametersof the raw material became 5.0 μm. The remaining raw materials and waterwere added into the pot having the first mixture therein, and then aresultant mixture was ball-milled for 7 hours to obtain a glazecomposition. A content of water is 40 parts by weight with respect to100 parts by weight of the solid matter of the raw materials. Theobtained glaze composition contains a glaze forming material having themedian diameter of 4.1 μm. The composition “B” of the glaze formingmaterial of Example 26 is shown in Table 1 by oxide conversion.

Next, the glaze composition was sprayed on a surface of an article of abase material for ceramic sanitary wares to form a layer of the glazecomposition thereon. The ceramic ware with the sprayed layer was bakedunder the same baking conditions as Example 1 to obtain a baked articlehaving a glaze layer of 0.6 mm thickness as the ceramic sanitary ware.

Examples 27, 28

In each of these Examples, a glaze composition was prepared according tothe same method as Example 2 except for the following features. That is,in Example 27, a ball-mill pot having a silica liner and alumina ballswere used for the ball-milling step. On the other hand, in Example 28, aball-mill pot having a alumina liner and alumina balls were used for theball-milling step. The obtained glaze composition contains a glazeforming material having the median diameter of 5.1 μm. The composition“B” of the glaze forming material of Examples 27 and 28 is shown inTable 1 by oxide conversion.

Next, the glaze composition was sprayed on a surface of an article of abase material for ceramic sanitary wares to form a layer of the glazecomposition thereon. The ceramic ware with the sprayed layer was bakedunder the same baking conditions as Example 1 to obtain a baked articlehaving a glaze layer of 0.6 mm thickness as the ceramic sanitary ware.

Example 29, Comparative Example 14

In Example 29, 3 parts by weight of a pigment (manufactured by KawamuraChemical Co., Ltd.; “GLAY 6501”) was further added to the glazecomposition of Example 2. On the other hand, in Comparative Example 14,3 parts by weight of the above pigment was further added to the glazecomposition of Comparative Example 1. The obtained glaze compositioncontains a glaze forming material having the median diameter of 5.1 μm.

Next, each of the glaze compositions was sprayed on a surface of anarticle of a base material for ceramic sanitary wares to form a layer ofthe glaze composition thereon. The ceramic ware with the sprayed layerwas baked under the same baking conditions as Example 1 to obtain abaked article having a glaze layer of 0.6 mm thickness as the ceramicsanitary ware.

With respect to each of the Examples 1 to 29 and Comparative Examples 1to 14, the following evaluations were carried out. Results are shown inTable 3 to 5.

(1) Antifouling Performance of the Glaze Layer

After the ceramic ware with the glaze layer was kept in a 5% alkaliaqueous solution at the temperature of 60° C. for 45 hours, it wascontaminated by a water-base paint. Then, it was tried to remove thecontamination from the ceramic ware with wastes. In Table 3 to 5, thesymbol “⊚” designates that the contamination was completely removed. Thesymbol “◯” designates that the contamination was almost removed, butthere was a case that a small amount of the contamination remained onthe ceramic ware. The symbol “X” designates that the remainingcontamination was visually identified.

(2) Degree of Luster of the Glaze Layer

The degree of luster of the glaze layer was visually compared with theglaze layer of Comparative Example 1. In Tables 3 to 5, the symbol “⊚”designates that the luster is better than that of Comparative Example 1.The symbol “◯” designates that the luster is substantially the same asthat of Comparative Example 1. The symbol “X” designates that the lusteris poorer than that of Comparative Example 1.

(3) Pore Generation Amount in the Glaze Layer

The pore generation amount of the glaze layer was visually compared withthat of Comparative Example 1. In Tables 3 to 5, the symbol “⊚”designates that the pore generation amount is smaller than that ofComparative Example 1. The symbol “◯” designates that the poregeneration amount is substantially the same as that of ComparativeExample 1. The symbol “X” designates that the pore generation amount islarger than that of Comparative Example 1.

(4) Degree of Semi-Opaque of the Glaze Layer

The degree of semi-opaque of the glaze layer was visually compared withthat of Comparative Example 1. In Tables 3 to 5, the symbol “⊚”designates that the degree of semi-opaque of the glaze layer is betterthan that of Comparative Example 1. The symbol “◯” designates that thedegree of semi-opaque of the glaze layer is substantially the same asthat of Comparative Example 1. The symbol “X” designates that the degreeof semi-opaque of the glaze layer is worse than that of ComparativeExample 1.

The results of Examples 1 to 9 indicates that the present invention canprovide the glaze layer having improved antifouling performance withoutdeteriorating the degrees of luster and semi-opaque of the glaze layerand increasing the pore generation amount, as compared with the glazelayer of the Comparative Example 1. Since the glaze layer of ComparativeExample 1 contains ZrSiO₄, it demonstrated poor antifouling performance.

In Comparative Examples 2 and 11, since the glaze layer contains anexcessive amount of the Si constituent, the antifouling performancedeteriorated and the pore generation amount increased. On the otherhand, in Comparative Example 3, since the content of the Sn constituentin the glaze layer is not sufficient, the visual beauty of thesemi-opaque glaze layer decreased. In addition, the antifoulingperformance deteriorated, and the pore generation amount increased.

In Comparative Examples 11 and 13, since the glaze layer contains anexcessive amount of the Al constituent, the degree of semi-opaque of theglaze layer decreased. On the other hand, in Comparative Examples 2 and10, since the content of the Al constituent in the glaze layer is notsufficient, the antifouling performance deteriorated, and the poregeneration amount increased.

In Comparative Example 3, since the glaze layer contains an excessiveamount of the Sn constituent, the antifouling performance deteriorated.On the other hand, in Comparative Example 12, since the content of theSn constituent in the glaze layer is not sufficient, the degree ofsemi-opaque of the glaze layer decreased.

In Comparative Example 7, since the glaze layer contains an excessiveamount of the divalent metal constituent, the antifouling performancedeteriorated, and the pore generation amount increased. On the otherhand, in Comparative Examples 6 and 11, since the content of thedivalent metal constituent in the glaze layer is not sufficient, thedegree of luster of the glaze layer decreased, and the antifoulingperformance deteriorated.

In Comparative Examples 4 and 8, since the glaze layer contains anexcessive amount of the monovalent metal constituent, the antifoulingperformance deteriorated, and the pore generation amount increased. Inaddition, the occurrence of cracking in the glaze layer was observed. Onthe other hand, in Comparative Examples 5 and 9, since the content ofthe monovalent metal constituent in the glaze layer is not sufficient,the degree of luster of the glaze layer decreased, and the antifoulingperformance deteriorated.

When the total amounts of the divalent metal constituents by oxideconversion in the glaze layer is 16 wt % or more, there was a tendencythat the improvement of antifouling performance is facilitated. On theother hand, when the total amounts of the divalent metal constituents is20 wt % or less, the pore generation amount was remarkably reduced.

In Examples 10 and 11 using the frit, the same evaluation results as thecases of Examples 1 and 2 were obtained. Additionally, in Examples 12and 13 that the particles of 30 μm or more were preliminarily removedfrom the raw material containing the Si constituent, the antifoulingperformance was further improved, as compared with the cases of Examples1 and 2, which are of the same compositions as the Examples 12 and 13.

In Examples 14 and 16 having the median diameter of the raw materialcontaining the Sn constituent within the range of 0.2 to 4.0 μm, theantifouling performance was further improved, as compared with the casesof Examples 3 and 4, which are of the same compositions as the Examples14 and 16. On the other hand, in Examples 15 and 17 having the mediandiameter of 0.2 μm or less, the antifouling performance wassubstantially equal to the cases of Examples 3 and 4, which are of thesame compositions as the Examples 15 and 17. The degree of semi-opaqueof the glaze layer of Examples 3 and 4 was better than that of Examples15 and 17.

In Example 18 having the median diameter of the glaze forming materialwithin the range of 4.0 to 5.0 μm, the antifouling performance wasfurther improved, as compared with the case of Example 2, which is ofthe same composition as the Examples 18. On the other hand, in Example19 having the median diameter of 4.0 μm or less, the antifoulingperformance was substantially equal to the case of Example 2.

In Examples 20 to 26 that at least one of the raw materials containingthe Si and Sn constituents was preliminarily grounded, the antifoulingperformance was further improved, as compared with the case of Example2, which is of the same composition as the those Examples. Inparticular, with respect to Examples 23 to 26, since the median diameterof the glaze forming material is within the more preferred range, thedegree of luster of the glaze layer was remarkably improved. Inaddition, in Examples 24 and 26 that the raw material containing the Snconstituent was preliminarily grounded, the degree of semi-opaque of theglaze layer was further improved.

In both of Example 27 using the alumina balls, and Example 28 using theball-mill pot with the alumina liner and the alumina balls, betterantifouling performance was obtained, as compared with the case ofExample 2, which is of the same composition as the Examples 27 and 28.In addition, the antifouling performance of the glaze layer of Example28 was better than that of Example 27.

In Example 29 using the glaze composition containing the pigment, acolored glaze layer other than semi-opaque was obtained. The glaze layerof this Example demonstrated substantially same evaluation results asthat of Example 2, which is of the same composition as the case ofExample 29 except that the pigment was not added. In addition, theantifouling performance was much better than that of Comparative Example14 containing the pigment.

With respect to the glaze composition of Examples 1 and 2 andComparative Example 1, an X-ray diffraction analysis was performed byuse of CuKα ray as the X-ray source. Results are shown in FIGS. 1A, 1B,2A, 2B, 3A and 3B. FIGS. 1A, 2A and 3A are measured X-ray diffractionprofiles of the Examples 1 and 2 and Comparative Example 1,respectively. The horizontal axis shows X-ray diffraction angle (2θ),and the vertical axis shows diffraction strength. In FIGS. 1B, 2B and3B, the term “peak data” shows a relation between the diffraction angleand the diffraction strength, which are determined from the measuredprofile of each of FIGS. 1A, 2A and 3A. The “card peak” shows therelation between the diffraction angle and the diffraction strength,which are determined from simulation results with respect to SnO₂crystal (FIG. 1B), SnO₂ and SnSiO₆ crystals (FIG. 2B), and zirconiumsilicate (FIG. 3B).

As understood from these figures, the glaze layer of Example 1 has onlydiffraction peaks resulting from SnO₂ crystal. The remainingconstituents are in amorphous state. Thus, when only SnO₂ is containedin the form of crystal in the glaze layer, a beautiful semi-opaque glazelayer with luster, smooth surface and good antifouling performance canbe obtained.

On the other hand, the glaze layer of Example 2 has only diffractionpeaks resulting from CaSnSiO₅ and SnO₂ crystals. The remainingconstituents are in amorphous state. Thus, when only CaSnSiO₅ and SnO₂are contained in the form of crystals in the glaze layer, a beautifulsemi-opaque glaze layer with luster, smooth surface, and goodantifouling performance can be obtained.

On the contrary, zirconium silicate crystals were generated in the glazelayer of Comparative Example 1. In this case, a beautiful semi-opaqueglaze layer can be obtained. However, as understood from the aboveevaluations, considerable surface unevenness of the glaze layer occurs,and the antifouling performance was poor.

As described above, a beautiful semi-opaque glaze layer with good lusterand excellent antifouling performance can be obtained by use of theglaze composition of the present invention. Even when a dirt deposits onthe glaze layer, the dirt can be easily removed from the glaze layer. Inaddition, the use of the glaze composition of the present inventionstably provides a smooth surface of the glaze layer, and a reduction inpore generation amount in the glaze layer. Moreover, when the glazelayer having a desired color other than semi-opaque is needed, it ispossible to readily provide a beautiful glaze layer having the desiredcolor and excellent antifouling performance by use of the glazecomposition of the present invention containing a required amount of thepigment.

In addition, an antifouling ceramic ware having the semi-opaque glazelayer with good luster and excellent antifouling performance can beproduced by forming a layer of the glaze composition of the presentinvention on a surface of an article of a base material for ceramicwares, and baking the layer at a temperature of 1150 to 1250° C. for 8hours or more to obtain a glaze layer on the surface of the bakedarticle.

Thus, since the glaze composition of the present invention can presentexcellent antifouling performance and beautiful appearance to theceramic wares, it will be preferably used in wide application areas ofceramics for home use, industry and architecture as well as artisticceramics, and particularly in the application areas of ceramic sanitarywares.

TABLE 1 Composition (parts by weight) A B C D E F G H I SiO₂ 60.0 65.567.0 55.2 58.9 60.0 62.3 58.2 62.8 Al₂O₃ 10.0 9.0 8.0 11.0 9.5 9.7 10.19.4 9.6 R₂O K₂O 2.0 2.5 2.4 2.8 3.5 2.0 2.4 2.2 2.7 Na₂O 2.0 2.5 2.2 2.52.3 2.0 2.2 1.9 2.5 Total 4.0 5.0 4.6 5.3 5.8 4.0 4.6 4.1 6.2 of R₂O ROCaO 10.0 11.8 11.6 11.7 9.9 10.1 9.2 9.8 11.8 ZnO 8.0 6.1 6.0 8.3 7.77.9 5.9 10.5 5.7 MgO 0.7 0 0 0.7 0.7 0.7 0 0.7 0 BaO 0 0 0 0 0 0 0 0 0Total 19.0 18.0 17.6 20.7 18.3 18.7 15.1 21.0 17.5 of RO SnO₂ 7.0 2.52.8 7.8 7.5 7.6 7.9 7.4 4.9 ZrO₂ 0 0 0 0 0 0 0 0 0

TABLE 2 Composition (parts by weight) J K L M N O P Q R S T U V SiO₂65.0 67.6 54.5 58.7 60.1 63.0 57.9 65.5 66.2 64.2 68.0 66.4 58.7 Al₂O₃8.0 7.9 11.3 9.5 9.7 10.2 9.3 9.0 9.5 7.9 12.0 9.4 11.2 R₂O K₂O 3.0 2.42.8 3.9 1.9 2.4 2.2 3.2 1.9 2.4 2.0 2.5 2.4 Na₂O 1.0 2.2 2.5 2.3 1.9 2.11.9 2.9 2.0 2.3 2.0 2.3 2.2 Total of R₂O 4.0 4.6 5.3 6.2 3.8 4.5 4.1 6.13.9 4.7 4.0 4.8 4.6 RO CaO 11.0 11.4 11.8 9.9 10.1 9.3 9.7 11.1 11.511.4 11.0 11.5 10.9 ZnO 3.0 6.9 8.3 7.7 7.9 4.5 11.0 4.1 2.8 4.9 3.0 4.99.2 MgO 1.0 0 0.7 0.7 0.7 0.6 0.7 0 0 0 0 0 0.7 BaO 0 0 0 0 0 0 0 0 3.00.8 0 0.9 0 Total of RO 15.0 17.3 20.8 18.3 18.7 14.4 21.4 15.2 17.317.1 14.0 17.3 20.8 SnO₂ 0 2.6 8.1 7.5 7.6 8.0 7.4 4.0 2.8 6.0 2.0 1.94.6 ZrO₂ 8.0 0 0 0 0 0 0 0 0 0 0 0 0

TABLE 3 EXAMPLE 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Glaze compositionA B C D E F G H I A B A B C C D Frit (wt %) Not used 30 30 Not usedContent (wt %) of 2 2 2 2 2 2 2 2 2 2 2 0 0 2 2 2 particles (more than30 μm) in SiO₂ raw material Particle size of SnO₂ 4.1 4.1 4.1 4.1 4.14.1 4.1 4.1 4.1 4.1 4.1 4.1 4.1 3.2 0.1 3.2 raw material (μm)Preliminary grinding Not performed Particle size after — — — — — — — — —— — — — — — — preliminary grinding (μm) Particle size of glaze 5.1 5.15.1 5.1 5.1 5.1 5.1 5.1 5.1 5.1 5.1 5.1 5.1 5.1 5.1 5.1 forming material(μm) Liner material of Silica ball-mill pot Ball material Silica Contentof pigment Not used Antifouling performance ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ⊚ ⊚ ⊚∘ ⊚ Luster of glaze layer ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ Poregeneration ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ amount Color (semi-opaque) of∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ glaze layer

TABLE 4 EXAMPLE 17 18 19 20 21 22 23 24 25 26 27 28 29 Glaze compositionD B B B B B B B B B B B B Frit (wt %) Not used Content (wt %) of 2 2 2 22 2 2 2 2 2 2 2 2 particles (more than 30 μm) in SiO₂ raw materialParticle size of SnO₂ 0.1 4.1 4.1 4.1 4.1 4.1 4.1 4.1 4.1 4.1 4.1 4.14.1 raw material (μm) Preliminary grinding Not SnO₂ SiO₂ SiO₂ SiO₂ SnO₂SnO₂ SiO₂ Not performed performed SnO₂ SnO₂ Particle size after — — —3.2 8.0 7.9 5.0 1.8 1.3 5.0 — — — preliminary grinding (μm) Particlesize of glaze 5.1 4.3 3.8 5.1 5.1 5.1 4.4 4.9 4.9 4.1 5.1 5.1 5.1forming material (μm) Liner material of Silica Silica Alumina Silicaball-mill pot Ball material Silica Alumina Alumina Silica Content ofpigment Not used 3 (parts by weight) Antifouling performance ∘ ⊚ ∘ ⊚ ⊚ ⊚⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ∘ Luster of glaze layer ∘ ⊚ ∘ ∘ ∘ ∘ ⊚ ⊚ ⊚ ⊚ ∘ ∘ ∘ Poregeneration amount ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ Color (semi-opaque) of ∘ ∘ ∘∘ ∘ ∘ ∘ ⊚ ⊚ ⊚ ∘ ∘ ∘ glaze layer

TABLE 5 COMPARATIVE EXAMPLE 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Glazecomposition J K L M N O P Q R S T U V J Frit (wt %) Not used Content (wt%) of particles (more 2 2 2 2 2 2 2 2 2 2 2 2 2 2 than 30 μm) in SiO₂raw material Particle size of SnO₂ raw 4.1 4.1 4.1 4.1 4.1 4.1 4.1 4.14.1 4.1 4.1 4.1 4.1 4.1 material (μm) Preliminary grinding Not performedParticle size after preliminary — — — — — — — — — — — — — — grinding(μm) Particle size of glaze forming 5.1 5.1 5.1 5.1 5.1 5.1 5.1 5.1 5.15.1 5.1 5.1 5.1 5.1 material (μm) Liner material of ball-mill pot SilicaBall material Silica Content of pigment Not used 3 (parts by weight)Antifouling performance X X X X X X X X X X X ∘ ∘ X Luster of glazelayer ∘ ∘ ∘ ∘ X X ∘ X X X X ∘ ∘ ∘ Pore generation amount ∘ X X X X X X XX ∘ X X X ∘ Color (semi-opaque) of glaze ∘ ∘ X ∘ ∘ ∘ ∘ ∘ ∘ ∘ X X X ∘layer

1. A glaze composition containing a glaze forming material, wherein amedian diameter after grinding and mixing of said glaze forming materialis within a range of 4 to 5 μm, and upon baking, said glaze formingmaterial forming a baked product comprising constituents: (a) 55.0 to67.0 wt % of SiO₂; (b) 8.0 to 11.0 wt % of Al₂O₃; (c) 2.0 to 8.0 wt % ofSnO₂; (d) 15.0 to 21.0 wt % of a divalent metal oxide; and (e) 4.0 to6.0 wt % of a monovalent metal oxide; with respect to a total weight ofsaid baked product.
 2. The glaze composition as set forth in claim 1,wherein said glaze forming material comprises, with respect to a totalweight of said glaze forming material, (a) 63.0 to 67.0 wt % of SiO₂;(b) 8.0 to 10.0 wt % of Al₂O₃; (c) 2.0 to 4.0 wt % of SnO₂; (d) 16.0 to20.0 wt % of a divalent metal oxide; and (e) 4.0 to 6.0 wt % of amonovalent metal oxide.
 3. The glaze composition as set forth in claim1, wherein the constituent (d) comprises, with respect to the totalweight of said glaze forming material, (d1) 10.0 to 12.0 wt % of CaOconversion; and (d2) 5.0 to 8.0 wt % of ZnO.
 4. The glaze composition asset forth in claim 3, wherein the constituent (d) comprises (d3) 1.0 wt% or less of MgO, with respect to the total weight of said glaze formingmaterial.
 5. The glaze composition as set forth in claim 1, wherein saidmonovalent metal oxide (e) comprises, with respect to the total weightof said glaze forming material, (e1) 1.0 wt % or more of Na₂O; and (e2)1.0 wt % or more of K₂O.
 6. The glaze composition as set forth in claim1, wherein said glaze forming material contains a frit, which isobtained by vitrifying a material containing at least one of theconstituents (a) to (e) and grinding the vitrified material.
 7. Theglaze composition as set forth in claim 1, wherein a material containingthe constituent (a) of said glaze forming material is a powder having aparticle size of 30 pm or less.
 8. The glaze composition as set forth inclaim 1, wherein a material containing the constituent (c) of said glazeforming material is a powder having a median diameter of 0.2 to 4.0 μm.9. The glaze composition as set forth in claim 1, wherein said glazeforming material is prepared by grinding a material containing at leastone of the constituents (a) and (c) to obtain a powder or a slurry, thenmixing materials containing the remaining constituents with said powderor said slurry, and grinding a resultant-mixture to obtain a powder ofsaid glaze forming material having a required particle size or a slurrythereof.
 10. The glaze composition as set forth in claim 9, wherein saidglaze forming material is prepared by grinding a material containing theconstituent (a) to obtain a powder having a median diameter of 5 μm orless or a slurry thereof, then mixing materials containing the remainingconstituents (b) to (e) with said powder or said slurry, and grinding aresultant mixture to obtain a powder of said glaze forming materialhaving a required particle size or a slurry thereof.
 11. The glazecomposition as set forth in claim 9, wherein said glaze forming materialis prepared by grinding a material containing the constituent (c) toobtain a powder having a median diameter of 1.5 to 2 μm or a slurrythereof, then mixing materials containing the remaining constituents(a), (b), (d) and (e) with said powder or said slurry, and grinding aresultant mixture to obtain a powder of said glaze forming materialhaving a required particle size or a slurry thereof.
 12. The glazecomposition as set forth in claim 9, wherein said glaze forming materialis prepared by grinding materials containing the constituents (a) and(c) to obtain a mixed powder having a median diameter of 5 μm or less ora slurry thereof, then mixing materials containing the remainingconstituents (b), (d) and (e) with said mixed powder or said slurry, andgrinding a resultant mixture to obtain a powder of said glaze formingmaterial having a required particle size or a slurry thereof.
 13. Theglaze composition as set forth in claim 9, wherein said glaze formingmaterial is prepared by grinding a material containing the constituent(a) to obtain a powder having a median diameter of 5 μm or less or aslurry thereof, then mixing materials containing the remainingconstituents (b) to (e) with said powder or said slurry, and grinding aresultant mixture to obtain a powder of said glaze forming materialhaving a median diameter of 4 to 5 μm or a slurry thereof.
 14. The glazecomposition as set forth in claim 9, wherein said glaze forming materialis prepared by grinding a material containing the constituent (c) toobtain a powder having a median diameter of 1.5 to 2 μm or a slurrythereof, then mixing materials containing the remaining constituents(a), (b), (d) and (e) with said powder or said slurry, and grinding aresultant mixture to obtain a powder of said glaze forming materialhaving a median diameter of 4 to 5 μm or a slurry thereof.
 15. The glazecomposition as set forth in claim 9, wherein said glaze forming materialis prepared by grinding materials containing the constituents (a) and(c) to obtain a mixed powder having a median diameter of 5 μm or less ora slurry thereof, then mixing materials containing the remainingconstituents (b), (d) and (e) with said mixed powder or said slurry, andgrinding a resultant mixture to obtain a powder of said glaze formingmaterial having a median diameter of 4 to 5 μm or a slurry thereof. 16.The glaze composition as set forth in claim 1, wherein the materialscontaining the constituents of said glaze forming material are ground bymeans of ball milling using alumina balls.
 17. The glaze composition asset forth in claim 1, wherein materials containing the constituents ofsaid glaze forming material are ground by means of ball milling using apot with an alumina liner and alumina balls.
 18. The glaze compositionas set forth in claim 1, comprising a pigment.
 19. An antifoulingceramic ware produced by forming a layer of said glaze composition asset forth in claim 1 on a dried base surface of a raw ceramic ware, andbaking said layer at a temperature of 1150 to 1250° C. for 8 hours ormore to obtain a glaze layer on a baked base surface of the ceramicware.
 20. The antifouling ceramic ware as set forth in claim 19, whereinan X-ray diffraction profile of said glaze layer has only diffractionpeaks resulting from SnO₂ crystal.
 21. The antifouling ceramic ware asset forth in claim 19, wherein an X-ray diffraction profile of saidglaze layer has only diffraction peaks resulting from CaSnSiO₅ crystal.22. The antifouling ceramic ware as set forth in claim 19, wherein anX-ray ray diffraction profile of said glaze layer has only diffractionpeaks resulting from crystals of SnO₂ and CaSnSiO₅.
 23. The antifoulingceramic ware as set forth in claim 19, wherein a thickness of said glazelayer is within a range of 0.2 to 1.2 mm.